1-First Step: Prepare Ingredients and Preheat Begin by preheating your oven to 350°F (175°C). Prepare all ingredients by chopping one small yellow onion finely and mincing 2 to 4 cloves of garlic. This mise en place ensures smooth workflow. Have all cheeses cream cheese softened, cottage or ricotta cheese ready, and mozzarella shredded within reach. Remove casing from sweet Italian sausage if needed, and measure out your spaghetti noodles.

2-Second Step: Cook the Meat and Aromatics Heat a large skillet over medium heat. Add 1/2 pound ground beef and 1/2 to 1 1/2 pounds of sweet Italian sausage (removed from casing). Brown the meat mixture thoroughly, breaking it up with a spatula. Season with salt and pepper for balance. Once browned, drain most of the grease to reduce excess fat. Next, add the chopped onion and minced garlic. Sauté until the onions turn translucent and fragrant, about 3-5 minutes. Stir in half (12 oz) of the marinara sauce into the meat mixture, combining for a rich, savory layer. Remove skillet from heat but keep warm.

3-Third Step: Cook Spaghetti Noodles Bring a large pot of salted water to a boil. Add 16 ounces dried spaghetti noodles and cook until al dente, usually about 8-10 minutes, depending on your pasta brand. Drain noodles and immediately toss with 3 tablespoons butter and the remaining half of the marinara sauce (12 ounces). This step ensures the noodles are well-coated, flavorful, and slightly moist. Save about ½ cup of the sauce if you prefer to toss noodles separately for better distribution.

4-Fourth Step: Prepare the Cheese Mixture In a mixing bowl, combine 8 ounces softened cream cheese, 1/4 cup sour cream, and 8 ounces cottage cheese or ricotta cheese. Mix thoroughly until smooth. Stir in 1 cup shredded mozzarella cheese and 3 teaspoons dried Italian seasoning if desired. This creamy, cheesy blend will add lusciousness and a delicate herbal note to the casserole.

5-Fifth Step: Assemble the Casserole Lightly butter a 9×13 inch (23×33 cm) baking dish. Optionally, lay half the butter slices on the bottom to add moisture and richness during baking. Spread half of the spaghetti noodles evenly across the dish. Layer the prepared three-cheese mixture evenly over the noodles. Top this with the remaining noodles in an even layer. Next, spread the cooked sausage and meat sauce mixture evenly over the top. Finish by sprinkling the remaining shredded mozzarella (1 to 2 cups) and 2/3 cup grated Parmesan cheese across the casserole. The layered setup mimics lasagna style but with spaghetti, ensuring a creamy, meaty bite in each serving.

6-Sixth Step: Bake to Perfection Bake the casserole uncovered in the preheated oven for 30-45 minutes. Keep an eye on the cheese; it should become hot, bubbly, and golden brown around the edges. If the cheese browns too quickly, loosely cover with foil to prevent burning. Baking allows flavors to meld and the three-cheese mixture to set into a rich, creamy texture.

7-Final Step: Rest and Serve Remove the casserole from the oven and let it rest for 10-15 minutes before serving. This pause helps the layers firm up, making it easier to cut and plate. Garnish with fresh basil or parsley if desired for a fresh herbal contrast. Serve warm for a comforting, satisfying meal.